• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文OA文献 >A. Computational chemistry applied to the analysis of air pollution reaction mechanisms ; B. Fundamental studies of droplet evaporation and discharge dynamics in electrospray ionization
【2h】

A. Computational chemistry applied to the analysis of air pollution reaction mechanisms ; B. Fundamental studies of droplet evaporation and discharge dynamics in electrospray ionization

机译：a.计算化学应用于空气污染反应机制的分析; B.电喷雾电离中液滴蒸发和放电动力学的基础研究

页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The first part of the thesis investigates the use of theoretical quantum chemical calculations for the study of the reaction pathways of the atmospheric aromatic-OH reaction. The computational model is comprised of a semi-empirical PM3 geometry optimization followed by a single point calculation performed using the Becke3LYP hybrid density functional and a 6-31G(d,p) basis. Zero-point energies were calculated using PM3, and transition states barrier heights estimated by a constrained optimization procedure developed for this study. Full mechanisms for the OH-initiated photooxidation of toluene, m-xylene, p-xylene, 1,2,4-trimethylbenzene and m-ethyltoluene are developed. The lowest energy intermediates have been determined and predicted products from these structures are compared to available experimental product data. These studies serve to refine proposed mechanisms currently available for toluene, mxylene and p-xylene, while providing new information on the 1,2,4-trimethylbenzene and m-ethyltoluene reaction pathways.ududIn the second part of the thesis, an experimental technique is described for probing the mechanism and dynamics of charged droplet breakup in electrospray ionization. At its core is an instrument that can perform simultaneous, in situ measurements of size and charge on individual droplets. Charged droplets are sampled directly from the spray source into a drift cell with a uniform electric field. A simultaneous diameter and charge measurement is made on individual droplets at the center of the cell using phase Doppler anemometry. By reversing the field in the drift chamber once the initial size and charge measurement is made, the droplet can be made to pass again through the measurement region of the phase Doppler anemometer. In this way, repeated measurements of the size and charge can be made on a single droplet. This technique has been applied to a variety of solutions used commonly in electrospray ionization and lead to the following generalizations. (1) The discharge dynamics of droplets with the same initial diameter and charge are highly reproducible for all solvents and analyte/solvent combinations studied to date. (2) Published over a hundred years ago, Lord Rayleigh's analysis of charged droplet instabilities resulting from solvent evaporation is remarkably accurate in predicting observed discharge events for all three solvents. (3) Droplet discharge events are characterized by loss of 15-20% of the charge from methanol and acetonitrile droplets, and 20-40% from water droplets, with little accompanying loss of solvent. (4) Discharge events occur in a reproducible temporal pattern, with decreasing time intervals between successive events, dictated by solvent evaporation and the approach to the Rayleigh limit. The droplet size decrease agrees well with a model of solvent evaporation. (5) The addition of biomolecules or salt (up to 10[superscript -3] M to the solution does not significantly alter discharge dynamics. The size-charge correlation and discharge dynamics of negatively charged droplets formed in electrospray ionization of 10[superscript -4] M NaCl in methanol are similar to those observed for positively charged droplets. (6) The life history of a single electrosprayed droplet can be followed through numerous discharge events (sequences with up to 50 measurements and 6 discharges have been observed) in the absence of radial confinement. This implies that no significant displacement of the droplet arises from discharge events and is inconsistent with any notion of high energy chaotic fission processes. (7) Droplet size-charge correlations show that, in certain instances, droplets from an electrospray fall into discrete groupings that can be attributed to fission events.ud
机译：论文的第一部分研究了理论量子化学计算在研究大气芳香族-OH反应的反应途径方面的应用。该计算模型包括一个半经验的PM3几何优化，然后使用Becke3LYP混合密度泛函和6-31G（d，p）进行单点计算。使用PM3计算零点能量，并通过针对该研究开发的约束优化程序估算过渡态势垒高度。建立了OH引发甲苯，间二甲苯，对二甲苯，1,2,4-三甲基苯和间乙基甲苯的光氧化反应的全部机理。已经确定了最低能量的中间体，并将这些结构的预测产物与可用的实验产物数据进行了比较。这些研究有助于完善目前对甲苯，二甲苯和对二甲苯可用的拟议机理，同时提供有关1,2,4-三甲基苯和间乙基甲苯反应途径的新信息。 ud ud在论文的第二部分，实验技术描述了探索电喷雾电离中带电液滴破裂的机理和动力学。它的核心是可以同时进行单个液滴大小和电荷的原位测量的仪器。带电的液滴直接从喷雾源采样到具有均匀电场的漂移池中。使用相位多普勒风速计，可以同时测量电池中心的单个液滴的直径和电荷。一旦进行了初始尺寸和电荷测量，通过反转漂移室中的电场，可以使液滴再次通过相位多普勒风速计的测量区域。以这种方式，可以在单个液滴上进行尺寸和电荷的重复测量。该技术已应用于电喷雾电离中常用的各种解决方案，并导致了以下概括。 （1）迄今为止，对于所有溶剂和分析物/溶剂组合，具有相同初始直径和电荷的液滴的放电动力学具有很高的再现性。 （2）发表于一百多年前，Rayleigh勋爵对由溶剂蒸发引起的带电液滴不稳定性的分析在预测所有三种溶剂的观察到的排放事件方面非常准确。 （3）液滴排放事件的特征是甲醇和乙腈液滴损失的电荷为15-20％，水滴损失的电荷为20-40％，而伴随的溶剂损失很少。 （4）放电事件以可再现的时间模式发生，连续事件之间的时间间隔不断缩短，这取决于溶剂的蒸发和接近瑞利极限的情况。液滴尺寸的减小与溶剂蒸发模型非常吻合。 （5）在溶液中添加生物分子或盐（至多10 [M -3] M不会显着改变放电动力学。电喷雾电离10 [M]-时形成的带负电荷的液滴的大小电荷相关性和放电动力学- 4]甲醇中的M NaCl类似于带正电荷的液滴所观察到的（6）单个电喷雾液滴的寿命历史可以通过多次放电事件（最多进行50次测量和观察到6次放电）进行跟踪。没有径向约束；这意味着液滴不会因放电事件而产生明显的位移，并且与高能混沌裂变过程的任何概念都不一致（7）液滴的大小与电荷的相关性表明，在某些情况下，来自电喷雾的液滴归因于裂变事件的离散组。 ud

著录项

  • 作者

    Smith James N.;

  • 作者单位
  • 年度 2000
  • 总页数
  • 原文格式 PDF
  • 正文语种
  • 中图分类

相似文献

  • 外文文献
  • 中文文献
  • 专利

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号